Microstructure and process characterization of laser-cold metal transfer hybrid welding of AA6061 aluminum alloy

Fiber laser-cold metal transfer (CMT) hybrid welding of an AA6061 aluminum alloy thin sheet was carried out. The microstructure was analyzed by an optical microscope, scanning electron microscope, and energy-dispersive spectrometry. The cross-weld tensile strength and hardness were tested to evaluate the mechanical properties of the welded joint. Accepted joints with finer microstructure and free of defects were obtained. The tensile strength was up to 223 MPa, 10 % stronger than that of a laser-pulse metal inert gas (PMIG) hybrid welded joint. Due to the featured CMT arc current waveform, stronger constitutional supercooling and more heterogeneous nuclei were generated in the weld pool of laser-CMT hybrid welding in comparison with laser-PMIG hybrid welding. It led to the results that the laser-CMT joint has a finer microstructure and narrower columnar dendrite zone compared with the laser-PMIG joint. Because of the stabilization of the CMT arc on the laser-induced keyhole, spatters were seldom found during laser-CMT hybrid welding and few hydrogen pores appeared in the joint.